Conventional serpentine fin machines make strips of fins by infeeding a flat sheet of metallic strip stock and outputting a series of metallic strips having corrugations therein. There are many uses for corrugate fin strips, particularly for vehicle components such as radiator, heater core, evaporator, and condenser fins, among others. The proper fin height is important for these components to allow for proper fin to tube brazing.
The typical fin machine generally works by feeding the continuous length of strip stock between at least one pair of form rollers having interleaved teeth to bend the strip and form corrugations (fins) in the stock. Two significant considerations, as they pertain to the shape of the corrugations, are the average height of the corrugations in a given length of fin stock and the typical variation in fin height from any one given fin to its adjacent fins (fin-to-fin variation). These two considerations are important to optimize the functioning of these fins when installed in the finished assembly.
The average height is generally determined by two main factors. The first factor is the shape of the form rollers and the spacing between the rollers, which determines the coarse average height of the fins. The second factor is the amount of tension imposed on the strip stock as it is fed into the form roller, which determines the fine average height adjustment of the fins.
The second significant consideration pertaining to the shape of the fins is the variation in fin-to-fin height, which is generally determined by the consistency of the tension applied to the strip stock as it is fed into the form roller. The more constant the tension, with minimal slight variations in tension, the more consistent the fin-to-fin height. If a problem exists and the desired tension is not held constant, then the fin-to-fin (convolution-to-convolution) height will jump up and down. Moreover, it is desirable to continuously measure the tension in the stock and immediately adjust it as necessary if it varies from the nominal tension desired (i.e., closed loop control).
One system used to maintain the proper tension is a pneumatic cylinder assembly which pinches the strip stock between a pair of cardboard pads to allow the frictional drag to create the tension. A fin machine employing a pneumatic cylinder is disclosed in U.S. Pat. No. 3,367,161. That machine employs a manually controlled pneumatic cylinder, along with other sets of spring loaded pressure pads, to control tension. However, it provides no automatic feedback, nor continuous monitoring of the actual tension in the stock. Current and past technology employing the pneumatic cylinder for tension has had no closed loop system for adjusting the cylinder pressure, particularly one that is capable of adjusting the required air pressure at the diminutive increments that are necessary in producing consistent corrugated fin heights. For example, a one inch wide strip of aluminum strip stock that is 0.003 inches thick may require only four pounds of tension, and adjustments in cylinder pressure need to be on the order of tenths of a pound. In fact, U.S. Pat. No. 4,753,096 ('096) and Japanese published application 63-101028 ('028) teach that pneumatic cylinders are not adequate for this job, and disclose employing an electronic control clutch brake to maintain the tension.
In order to allow for closed loop control, these systems have moved away from the use of a pneumatic cylinder and the tension control is handled by the electronic control, such as a solenoid controlled braking roller as disclosed in the '028 application or a magnetic particle clutch brake as disclosed in the '096 patent. However, for these configurations, difficulties arise not only in the minimum size material that generally can be handled, but by the many points at which tolerances and wear can creep into the system and affect the fin-to-fin height consistency. Having many locations of potential problems makes trouble shooting a machine difficult and time consuming.
While both electronic brakes allow for closed loop control, one of the concerns associated with employing these electronic types of clutch brakes is that they generally do not maintain consistent enough tension for many fin forming applications. Both require at least two rollers to perform the braking action that creates the tension. Tension fluctuations, then, can be created by such things as non-concentric clutch rollers (out-of-round) and by wear on the bearings that mount these rollers, surface wear on the rollers themselves, and inconsistencies within the clutch itself such as inconsistencies in the clutch bearings. These are relatively expensive parts to repair or replace.
Additionally, the '096 patent design tends to require a complicated electronic set up to regulate it, having many parts that can fail or be out of tolerance. A magnetic particle clutch arrangement also is relatively expensive just with the cost of the clutch itself, the big roller cylinders and the associated, relatively complicated electronic circuitry.
Also, generally the minimum thickness of aluminum material that a magnetic particle clutch, large enough to operate continuously while forming fins, can effectively handle for a nominal one inch wide strip is about 0.004"-0.005" since there is so much built in resistance to the clutch/roller configuration. The minimum tension which the clutch will allow even if the clutch is shut off can be too great for thinner aluminum strip stock such as 0.003" thick. This is a disadvantage because thinner material, when used in applications such as vehicle condensers, allows for less weight on the vehicle and lower material costs.
Thus, it is desirable to have a fin forming machine which allows for accurate and easily adjustable average fine height adjustment and also maintains consistent fin-to-fin height with minimal variation, while minimizing the cost and complexity of the system.